The number of people in the world relying on manual wheelchairs for primary mobility has grown significantly in the past few decades and is approximated to be near two million in the United States alone. Unfortunately, traditional wheelchair pushrims have some disadvantages, including that they may cause physical injury to users, make pushing difficult, are unnecessarily heavy and difficult to install, vibrate uncomfortably, provide poor grip, and make braking painful on the hands. For example, the pushrims on traditional wheelchairs leave a gap between the wheel and the pushrim. Occasionally, body parts such as the wheelchair user's thumbs can slip into the gap, causing the thumbs to hit the wheel and spokes, resulting in injury to the user. Use of traditional pushrims can also result in long-term injury to the shoulders, hands, and wrists. It should be noted that the terms “pushrim” and “handrim” are used interchangeably in the field.
Secondary injuries such as carpal tunnel syndrome (CTS) are prevalent in manual wheelchair users with some studies finding up to 63% prevalence (Aljure, et al, “Carpel Tunnel Syndrome in Paraplegic Patients” Paraplegia 23; International Medical Society of Paraplegia (1985)). Nonetheless, users must use their arms in almost every daily activity and the option of a power wheelchair to prevent overuse injuries is often not economically feasible and undesirable for other reasons. Although there are several CTS-preventative propulsion devices commercially available (for example, add-on lever crank devices), the high prevalence of injury remains. Further, the best clinical solutions to relieve some of the injuries leave individuals unable to self-propel for extended periods of time. For example, the best resolution to CTS, carpal tunnel release surgery, often leaves an individual unable to self-propel or work for weeks and some times months. Thus, because of the limited options available, most manual wheelchair users ignore pain and trauma to their hands and arms during propulsion and continue the everyday activities, regardless of the risk of long-term harm. These phenomena have prompted research establishing a nexus between wheelchair propulsion biomechanics and highly prevalent secondary injuries.
In studies investigating secondary upper extremity injuries, the high prevalence of injuries has been attributed in part to overuse of the arms during daily wheelchair propulsion. Many researchers believe the inefficient transmission of power from the hand to the pushrim is a factor that contributes to nerve dysfunction in the upper extremities. Several studies on CTS in the able-bodied working population have found that long-term exposure to high repetitious forces to the hand and wrist can cause CTS (Silverstein et al, “Occupational Factors and Carpal Tunnel Syndrome” American Journal of Industrial Medicine; Vol. 11 (1987)). Recent studies on wheelchair propulsion biomechanics relate CTS in manual wheelchair users to higher propulsion forces applied to the pushrim and to greater stroke frequency during wheelchair propulsion (Baldwin et al “A Relationship between Pushrim Kinetics and Median Nerve Dysfunction).
Unfortunately, the tube diameter of standard pushrims is too small to allow complete grip between the palm of the hand and the fingers. The hand contacts only a small area of the surface of the rim, therefore lacking the friction to provide effective pushing grip. This creates a number of problems. First, it reduces the contact area between the hand and the pushrim, which increases the pressure on the contact points of the hand, and increases the forces transmitted to the delicate structures of the hand. Second, the inability to grip the pushrim with the entire palm and fingers reduces the mechanical efficiency by recruiting muscles for stabilization on the rim instead of delivering power to the wheelchair. Thus, the decreased mechanical efficiency and increased forces while using standard pushrims may contribute to developing secondary injuries like CTS. A wheelchair pushrim system capable of reduced injury risk, increased ease of pushing and installation, lighter weight, increased pushing friction, and decreased braking friction, would be highly desirable.
The inventors of the present application patented an improved pushrim, described in U.S. Pat. No. 6,276,705. That pushrim added a second tube located concentrically inside the first tube so that there would be additional surface area, namely the ring along the second tube, for the hand to contact, thereby increasing mechanical efficiency. The patent also describes an S-shaped trough attached to the upper surface of the first tube. While a genuine improvement over existing technology, the assembly suffers the disadvantages of being complicated to assemble and adding weight to the rim assembly.
A primary object and feature of the present invention is to provide a wheelchair pushrim system better contoured to a wheelchair user's hand. Another object of the present invention is to provide increased friction for improved pushing. Yet another object is to provide a wheelchair rim system that is lighter weight and is easier to assemble than those in the prior art. Another object of the present invention is to provide a decreased friction surface for more comfortable braking. Another object of the present invention is to provide a system that will help prevent injuries to fingers, hands, arms, and shoulders. Another object of the present invention is to provide a system that is efficient and requires reduced time, money, and energy. Other objects and features of this invention will become apparent with reference to the following descriptions.